The present invention relates to a CRT (cathode-ray tube) display apparatus, and more particularly to a cursor display in a character display apparatus of a raster scanning type.
A character display apparatus with a CRT display has been widely used as a man-machine communication device in a computer system. When, for example, it is desired to enter new data into the computer or to edit or correct data which has already been entered therein, an operator operates such a display apparatus so that required data may appear on its screen, and replaces or changes the data with new data one by one with the aid of a keyboard or the like by viewing the screen. The display apparatus used for such applications requires a cursor display for indicating on the screen a position of data to be inserted or altered.
A typical CRT display apparatus includes a refresh memory for storing data to be displayed which corresponds to a frame of image. The input and output of data between the refresh memory and external information sources such as the computer, keyboard or the like are controlled by an input/output control part. A timing control part provides the generation of display addresses for sequentially reading the contents of the refresh memory for the purpose of display, and provides various timing controls for display. The display of a cursor is effected by controlling a video signal at a timing at which the display address produced by the timing control part coincides with a data entry position selected by the input/output control part. The cursor display causes the character to be provided with an under-line or a block indication there-around. The cursor display may be blinked to make the cursor striking to the viewer, as disclosed in U.S. Pat. No. 3,531,796. The display apparatus used defines the number of characters which can be displayed, the size of them, the spacings of the characters on lines, etc., and these conditions determine the use of one of the various cursor displays as mentioned above.
Recently, microprogramming controls in each part of the display apparatus have been put into practice. This makes it possible to provide a display apparatus whose capacity of display characters or whose display functions can be made different by the alteration of the program with the same timing control part used. In this case, the cursor display is often required to be unique corresponding to the individual display apparatus to be used. The use of many cursor display circuits in conformance with the respective requirements, however, results in a loss of the merit of the microprogramming control which allows the reduction of hardwares and the production of high cost performance with the hardware made common to many devices.